Not Applicable.
Not Applicable.
The present invention relates generally to radar systems, and more particularly, to radar systems for aircraft.
The use of radar for guiding aircraft to land and take off is well known in the art. A radar transmits signals and processes the signal returns to ascertain the heading and altitude of an aircraft approaching an airport. The radar information is used to maintain the aircraft at or near an optimal flight path for landing the aircraft. The level of reliance on radar can vary based upon the weather conditions. In cases where visibility is severely limited, a pilot can rely very heavily on radar information to land the aircraft.
In one type of landing system, known as Precision Approach Radar (PAR), a radar operator verbally guides the pilot along a landing course line and a landing glide slope, collectively called the landing flight path, based upon radar data. The PAR system presents the radar operator with a pair of two-dimensional displays. One display provides an aircraft course line in an azimuth display, and the other display provides an aircraft glide slope in an elevation display. The aircraft azimuth and elevation are plotted against range from the airport. On the two display formats, radar returns corresponding to the actual landing flight path of the aircraft are overlaid with lines depicting the optimal landing flight path of an aircraft at a particular runway. The optimal landing flight path may be different at different airports, or at the various runways at a particular airport, or from time to time depending upon weather conditions, or for different types of aircraft.
The PAR system operator evaluates the aircraft""s position versus the optimal landing flight path using the azimuth and elevation radar displays and verbally informs the pilot via radio about the current position and trend of the aircraft relative to the optimal landing flight path. The verbal instructions typically include predefined terms, e.g., well above glide slope, slightly right of course line, on course, etc., to indicate the relative position of the aircraft. The pilot then adjusts engine speed and control surfaces, e.g., rudders, to conform to the optimal landing flight path based upon the radar operator""s instructions.
While standardized terminology can be used, the meaning of the terms of the verbal flight instructions are imprecise and can vary from operator to operator. In addition, a given operator may subjectively vary the instructions over the landing process. For example, a PAR operator generally pays closer attention as the aircraft moves closer to the airport so as to provide finer control as the aircraft nears touchdown.
In addition, an operator""s choice of radar display scale can also affect operator judgment. For example, a zoomed out display is typically used to provide initial guidance of an aircraft while far from the airport. In contrast, a zoomed in display, often used for aircraft close to the airport, is needed to provide fine resolution and fine flight path correction. It is relatively difficult for an operator to use the PAR terminology consistently for multiple zoom levels.
Another disadvantage associated with known PAR systems results from unprocessed radar measurements relative to the position of the radar. For safety reasons, the radar antenna is located at a predetermined distance from the touchdown point of the runway, often nearly a mile back from the touchdown point. For such an offset radar, the angular change indicated by the unprocessed radar data for an airplane exactly on a straight landing flight path is relatively large as the aircraft approaches touchdown. Where the optimal landing flight path is straight, unprocessed raw radar data indicates the optimal landing flight path as curved downward. Thus, to provide a more intuitive straight landing flight path display, the raw radar data is processed through coordinate transformations that have the effect of converting to Cartesian coordinates and re-positioning the coordinate origin at the touchdown point, thus making the optimal landing flight path appear straight on the radar displays.
Several factors degrade the radar accuracy for displayed points near the touchdown point. As described, the radar transmitter is physically offset from the touchdown point for safety reasons. The offset is both in the x direction, along the runway axis, and along the y direction, along an axis perpendicular to the runway. Because the radar transmitter is physically offset from the touchdown point, as the aircraft approaches the touchdown point the elevation angular accuracy, due to x axis offset, and the scan angle accuracy, due to y axis offset, both become increasingly dominant in the determination of the actual flight path of the aircraft. One of ordinary skill in the art will recognize that the elevation angular accuracy of a typical PAR radar system is about a tenth of a degree. A tenth of a degree elevation error results in a substantial percentage error in the reporting of the detected elevation of the aircraft as it approaches the touchdown point. One of ordinary skill in the art will also recognize that the radar scan angle width increases as the aircraft altitude decreases causing a reduction in the resolution of the radar near the touchdown point. Deviations from the flight path near the displayed touchdown point are scaled to less than a pixel on the display. Deviations of only a few pixels on a moving target can be difficult to detect by the radar operator.
Operator provided instructions have an inherent latency due to the time that is required for the operator to interpret the displayed radar information and make a decision as to what information should be given to the pilot. Such latency can cause the pilot to overcompensate or oscillate about the optimal flight path. Additionally, even with standard informational phrases, the transformation from the radar display to the verbal phrase is subjective, and thus, variable operator to operator.
Further, the radar operator is in a high stress environment. The operator must attempt to issue verbal information to the aircraft pilot at intervals of approximately 5 seconds as the aircraft approached landing. Under this stressful environment, inaccurate information may be issued by the operator.
It would, therefore, be desirable to provide a PAR landing system that presents standardized and consistent spatial information to a pilot during a landing approach.
The present invention provides computer generated pilot instructions during the landing process. With this particular arrangement, pilots receive objective landing instructions that eliminate operator inconsistencies and human limitations. While the invention is primarily shown and described in conjunction with landing aircraft, it is understood that the invention is generally applicable to systems in which it is desirable to provide computer generated information based upon the path of a moving object in relation to a desired path.
In one aspect of the invention, a method for automatically providing instructions to a pilot for landing an aircraft includes determining spatial information at a radar station that corresponds to a spatial difference between an actual landing flight path of the aircraft and an optimal landing flight path. The method further includes converting the spatial information to flight instructions and conveying the flight instructions to the pilot for enabling the pilot to correct the actual landing flight path to the optimal landing flight path.
The flight instructions to the pilot can be generated as synthesized voice flight instructions that correspond to the spatial information. The synthesized voice flight instructions are conveyed to the pilot to facilitate landing of the aircraft. The use of synthesized voice flight instructions provides spatial information to the pilot that is more consistent and more accurate than conventional voice information from a PAR radar operator.
In a further aspect of the invention, an apparatus for automatically generating pilot landing instructions includes means for computing a spatial difference between an actual landing flight path of the aircraft and an optimal landing flight path. The apparatus also includes means for converting the spatial information to flight instructions and conveying the flight instructions to the pilot for enabling the pilot to correct the actual landing flight path to the optimal landing flight path.